<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <style>
        div {
            height: 500px;
        }
        
        .aside {
            width: 300px;
            float: left;
            background: yellow;
        }
        
        .main {
            overflow: hidden;
            background: aqua;
        }
    </style>
</head>

<body>
    <div class="aside"></div>
    <div class="main"></div>
</body>

</html>